Very nice! That is one of the nicest home-made boxes I have seen from someone who is not a professional audio installer person. Actually, its nicer than some that are manufactured.
Very nice job on the carpet! I HATE carpeting boxes, they always turn out so crappy on the edges for me. I guess it takes alot of patience... and glue
You are very brave to leave the wires exposed to the rear. Even if there are no people in the back seat, I might have cargo sliding around back there knocking against the wires. I see why the amp is positioned this way though, for the accessibility of the controls. Any thoughts on turning the amp sideways to guard the wires in the rear? I think the controls might still be somewhat accessible from the side under the seat. In any event, the amp is easily movable by your friction mounted design (carpet on carpet).
Great design!!!